Moving Average Convergence Divergence (MACD)


Developed by Gerald Appel, MACD is one of the simplest and most reliable indicators available. MACD uses moving averages, which are lagging indicators, to include some trend following characteristics. These lagging indicators are turned into a momentum oscillator by subtracting the longer moving average from the shorter moving average. The resulting plot forms a line that oscillates above and below zero.

The most popular formula for the standard MACD is the difference between a stock's 26-day and 12-day exponential moving averages. However Appel and others have since tinkered with these original settings to come up with a MACD that is better suited for faster or slower securities. Using shorter moving averages will produce a quicker, more responsive indicator, while using longer averages will produce a slower indicator.

What does MACD do?
MACD measures the difference between two moving averages. A positive MACD indicates that the 12-day EMA (exponential moving average) is trading above the 26-day EMA. A negative MACD indicates that the 12-day EMA is trading below the 26-EMA. If MACD is positive and rising, then the gap between the 12-day EMA and the 26-day EMA is widening. This indicates that the rate-of-change of the faster moving average is higher that the rate-of-change for the slower moving average. Positive momentum is increasing and this would be considered bullish. If MACD is negative and declining further, then the negative gap between the faster moving average and the slower moving average is expanding. Downward momentum is accelerating and this would be considered bearish. MACD centreline crossovers occur when the faster moving average crosses the slower moving average. One of the primary benefits of MACD is that it does incorporate aspects of both momentum and trend in one indicator. As a trend following indicator, it will not be wrong for long. The use of moving averages ensures that the indicator will eventually follow the movements of the underlying security.

As a momentum indicator, MACD has the ability to foreshadow moves in the underlying stock. MACD divergences can be a key factor in predicting a trend change.  For example a negative divergence on a rising security signifies that bullish momentum is wavering and that there could be a potential change in trend from bullish to bearish. This can serve as an alert for traders and investors.

In 1986 Thomas Aspray developed the MACD histogram in order to anticipate MACD crossovers. The MACD histogram represents the difference between MACD and the 9-day ema of MACD. The plot of this difference is presented as a histogram, making centreline crossovers and divergences more identifiable. Sharp increases in the MACD histogram indicate that MACD is rising faster than the 9-day ema and bullish momentum is strengthening. Sharp declines in the MACD histogram indicate that the MACD is falling faster that its 9-day ema and bearish momentum is increasing. Thomas Aspray recognised the MACD histogram as a tool to anticipate a moving average crossover. Divergences usually appear in the MACD histogram
before MACD moving average crossover. Armed with this knowledge, traders and investors can better prepare for potential change. Remember the weekly MACD histogram can be used to generate a long-term signal in order to establish the tradable trend, thus allowing only short-term signals that agree with the major trend to be used for investment action. 2007
Christopher M. Quigley B.Sc., M.M.I.I., M.A.